Fluorescent panel lamp coating



Aplll 19, 1966 w. c. MARTYNY 3,247,415

FLUORESCENT PANEL LAMP COATING Filed May 1, 1961 F g1. X/

OOCQOU DDOOOO DOOOOU ilOODO- Inven'tov: 8 WiLLiam (1M wi ng His A torney United States Patent Ofiflce 3,247,415 Patented Apr. 19, 1966FLUORESCENT PANEL LAMP COATING William C. Martyny, Lyndhurst, Ohio,assignor to General Electric Company, a corporation of New York FiledMay 1, E61, Ser. No. 1%,822 6 Ciaims. (Cl. Mil-W9) This inventionrelates to fluorescent panel lamps generally and more particularly tothe phosphor coating thereof.

In fluorescent panel lamps, the discharge path is a labyrinthine channelformed between two vitreous components sealed together along theirmargins. Such lamps provide a relatively long discharge in a small areawhich is an advantage from the point of view of compactness of sourceand ease of handling. They offer what may be described as an area lightsource as against a line source as is the case with the usual elongatedfluorescent lamp.

In many of the applications presently visualized for a panel lamp, it isintended that only one face of the lamp be exposed to view. Forinstance, it is contemplated that panel lamps be made in modular sizescorresponding to the dimensions of standard ceiling tiles.Alternatively, it is contemplated that panel lamps be used in shallowfixtures. In either case, the lower plate, which may be referred to asthe faceplate of the lamp is exposed to view and an attractive uniformappearance is desired for it. Fluorescent panel lamps, like anyfluorescent lamp, are coated internally with a phosphor. The visualappearance therefore depends in large part on the quality and uniformityof the phosphor coating.

The object of the invention is to provide a fluorescent panel lampphosphor coated in such fashion as to result in a product of attractiveappearance particularly as regards the faceplate.

Another object of the invention is to provide a novel process forphosphor coating 21 fluorescent panel lamp.

The panel lamp with which the present invention is particularlyconcerned is formed by sealing two molded glass plates, the faceplateand the backplate, together along their margins. The upper components,referred to as the backplate, is molded to define, in cooperation withthe faceplate, a labyrinthine discharge channel by means of parallelgrooved sections or channelways extending side by side and joinedtogether at alternate ends. The faceplate may be provided with aplurality of shallow embossments of square outline giving it somewhatthe appearance of a quilt or checkerboard. The flat areas or lands ofglass at the base of the partitions in the backplate are designed toseat on corresponding flat areas or lands between the embossments in thefaceplate.

In accordance with my invention, I coat both the faceplate and thebackplate with phosphor before they are sealed together along theirmargins. Desirably the phosphor coating is lehred prior to sealing theplates together. This makes it possible to have phosphor present on theentire faceplate, including the flat areas or lands under the partitionsof the backplate, and such phosphor coating is free of binder or organicmaterial which would contaminate the lamp.

In a preferred process according to my invention the backplate is coatedby flowing a phosphor suspension over it, then overturning the plate toallow the excess suspension to drain off along the edges or flats of theinternal partitions. After drying, the phosphor is wiped off from themargin and from the flats of the partitions. The faceplate is similarlytreated but the phosphor is wiped off from the margin only. The platesare preferably assembled and sealed together in such fashion that anydrainage patterns are parallel in both plates and not crossed.

For other features and. for further objects and advantages of theinvention, attention is now directed to the following description of apreferred embodiment of a lamp and of the coating process therefor, tobe taken in conjunction with the accompanying drawing. The features ofthe invention believed to be novel will be more particularly pointed outin the appended claims.

In the drawing:

FIG. 1 is a side sectional view of the backplate of a square panel lamphorizontally disposed for filling with phosphor suspension.

FIG. 2 is a similar view showing the lamp inverted at an oblique angleto allow thephosphor suspension to drain out.

FIG. 3 is a plan view of the inside of the backplate coated withphosphor.

FIG. 4 is a plan view of the inside of the faceplate coated withphosphor.

. FIG. 5 is a cross section through the lamp taken along line 5-5 inFIG. 6.

FIG. 6 is a plan view of the coated and assembled lamp looking at thefaceplate.

Referring to the drawing, there is shown at 1 in FIG. 1 to 3 thebackplate of a six-channel fluorescent panel lamp. The complementaryfaceplate which forms the underside of the lamp exposed to view when thelamp is mounted in a fixture or incorporated into a ceiling, is shown at2 in FIG. 4. When sealed together alongv their margins, the two platesform the generally flat square panel lamp shown at 3 in FIGS. 5 and 6.Both plates may be formed from flat sheets of glass by any suitablemeans, for instance by vacuum molding or by pressing. The uppercomponent or backplate is molded to define, in cooperation with thefaceplate, a winding or labyrinthine discharge channel or passage bymeans of six parallel grooved sections or channelways 4 extending sideby side and joined together at alternate ends, as at 5 where thelengthwise folds formingpartitions 6 end, thereby forming a continuousgrid-like channel. The faceplate is provided with a plurality of shallowembossments 7, of square outline in plan view, giving it somewhat theappearance of a quilt or checkerboard. The quilting 0f the faceplateimproves its appearance, increases the strength of the assembly, andmakes for a more uniformly lighted face. FIGS. 3 and 4 are of courseviews of the inside surfaces of these plates and it is intended that theflats or lands 6 between channelways seat on the corresponding lands 8extending between embossments in the faceplate.

In order to phosphor-coat the backplate, it may be supportedhorizontally as indicated in FIG. 1, preferably over a suitable pan tocat-ch any overflow, and the phosphor suspension poured into it to theoverflow point as indicated at 9. The purpose is to paint or coat theentire inside surface of the backplate with phosphor suspension or paintand the same result may be achieved by spraying in excess. For thepurpose of the present invention, the kind of phosphor used or the typeof binder forming the suspension is not important. The phosphors mostcommonly used are calcium halophosphates activated with manganese orantimony. For the suspension I prefer to use a water soluble binderconsisting of an ammoniaca'l aqueous solution of the copolymer of methylvinyl ether and rnaleic anhydricle (PVM/MA) and of polyacrylic acid(PAA), as disclosed and claimed in my copending application Serial No.12,969, filed March 7, 1960, entitled Phosphor Coating Method andassigned to the same assignee as the present invention, now Patent3,006,781. However other binder solutions may be used, such as forinstance the nitro binders at one time commonly used in fluorescent lampmanufacture and consisting of a solution of nitrocellulose in butylacetate.

The back-plate is then tipped over and overturned and inclined asindicated in FIG; 2 with the lands 6 extending up and down. The majorpart of the contents naturally fall out as soon as tipping is begun butthen drainage continues I while the plate is inclined as indicated andwarm air is blown upon it to 'drythe coating. By running the lands upand down, the excess tends to drain out of the grooves or channelwaysand to run along the lands, either all the way to the lower margin at.10, or to the terininations of the lands as at 11. The coating driesout first where it is thinnest and this is in the bottoms of thechannelways. The coating dries out last and thickest along the lands andmargins and this is where streaks and irregularities are likely tooccur. However this is not important because after thorough drying, thelands 6 and the entire margin of the lamp including the bottom margin10, the side margins 12, 13 and the top margin 14 are wiped or brushedclear of phosphor. The angle A at which the backplate is held to thevertical is notcritical; what is desired is that the coating drain outfairly rapidly without pooling anywhere, and it should drip off at theend of the land at 11 rather than running around the loop at and forminga flow streak. For the illustrated backplate, an angle A ofapproximately 60 is suitable.

The coating of the faceplate is done in similar fashion. It is generallydesirable to have the lamp emit a greater proportion of its lightdownwardly through the faceplate than through the backplate; Therefore agenerally thinner phosphor coating is desired on the faceplate and thisis readily accomplished by using a less viscous binder solution. Incoating the faceplate, the coating will likewise thin out and dry outfirst and most evenly in the embossmeiits 7; This is desirable becausethe emlbossments are the partswhich naturally strike the eye first. Thedrainage winpccur primarily along the lands 8 from the top (margin 15towards the bottom margin 16. Any flow streaks that occur in thefaceplate will be relatively minor and will occur on the lands 8 runningin a direction parallel to the side margins 17, 18. The phosphor coatingwill tend to be somewhat thicker along the lands in the direction offlow but this is not objectionable for"a reason which will appearshortly. After drying, only the margins of the faceplate are wiped clearof phosphor. The phosphor coating is indicated by the speckling in FIGS.3 and 4.

To make a fluorescent panel lamp, the phosphor is lehred, that is heatedto a sufiiciently high temperature to decompose and drive out theorganic binder, and the backplate and faceplate are mated and sealedalong their margins to form an envelope. This envelope is provided withdischarge supporting electrodes 19, 20 at the ends of the channel, andwith an ioniza'ble filling consisting of a vaporiz'able metal such asmercury and an inert gas such as argon. In the usual fluorescent lampconfiguration, the filling is an excess of mercury to provide a partialpressure of 5 to 8 microns during normal operation, and argon at apressure of 2 to 3 millimeters. Such a filling provides in generaloptimum generation of 2537 A. radiation for excitation of the phosphorcoating. In general I prefer to have the plates sealed together with aledge seal and the lamp to be made according to the teachings of thecopending application of Richard S. Christy, Serial No. 106,829, filedof even date herewith, entitled Panel Lamp and Manufacture Thereof, andassigned to the same assignee as the present invention.

According to a feature of my invention, in assembling the backplate andfaceplate for sealing, I match the direction of phosphor flow ordrainage in the two plates,that is, side margins are mated together.Mating of a side margin to a bottom or top margin is avoided." Thisavoids icrossed streak lines and makes for better appearance. In coatingthe plates, the phosphor coating generally dries somewhat thicker at thebottom end than at the top end. I fiind it then preferable to place'thetop or thin end of the faceplate so that it overlies the elec- 7 of thefaceplate.

1 According to another feature of my invention, the phosphor coatingextends over the entire faceplate including the lands 8 in the faceplatewhich overlie (or underlie in FIG; 5)- the lands din the backplate. Inthe sealing method according to the aforementioned Christry application,fused ledge seals are formed at the margins as indicated at 21 in FIG.5, by the application of tremendously high sealing pressures while theglass is heated above the strain point but below the softening point.However at the internal partitions or lands 6, 8 the glass is merelypressed into close conformance by the application of relatively lowpressure. This is sufiicient to prevent the are from leaking through orshort-circuiting at the junctions under the partitions. Thus phosphor onthe lands of the faceplate is imprisoned between the glass surfaces inthese regions, as indicated by the dotted inside lining in FIG. 5. Thisis highly desirable for the sake of appearance; in the absence ofphosphor under the lands, clear glass results which stands out darkly insharp and disagreeable contrast, especially when the lamp is not lit.The somewhat greater thickness of phosphor along the lands of thefaceplate is therefore not objectionable but is in fact desirable sinceit results in a lamp with a' faceplate of more uniformly Whiteapperance. I prefer to wipe the phosphor off the lands of the backplateto avoid build-up of an excessive thickness. Since the coating is in anycase somewhat thicker over the lands of the faceplate than in theembossments, a fully adequate thickness of phosphor is present. p

The notches at 22 in the seal close to the electrodes on the faceplateside are for the purpose of attaching bases to the ledge seal on thebackplate side by means of metal clips. Such bases may be of the kinddescribed and claimed in copending application Serial No. 106,827, ofAlbert F. Pate, Robert A. Kuebler and Harold R. Kestner, filed of evendate herewith, entitled Panel Lamp Base, and assigned to the sameassignee as the present invention. The inleads 23, 24 of the electrodes19, 20 will then be connected to the terminals or contact pins of thesebases.

While a specific embodiment of the inventionas regards structure andprocess has been described in detail and illustrated, same is intendedby way of example only and not in order to limit the invention thereto.Modific'ations will readily occur to those skilled in the art and it isintended by the appended claims to cover any such as fall within thetrue'spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A fluorescent panel lamp comprising a vitreous envelope formed by abackplate and a faceplate sealed together along their margins, saidbackplate having grooved channelways extending therein with partitionsbetween them to define a labyrinthine discharge channel, and a phosphorcoating extending over the entire faceplate including the areasunderlying and engaging the partitions in said backplate.

2. A fluorescent panel lamp comprising a vitreous envelope formed by abackplate and a faceplate sealed together along their margins, saidbackplate having a plurality of grooved channelways extendingthereinside by side with partitions between them and joined at alternateends to, define a labyrinthine discharge channel, said faceplate havinga' plurality of shallow embossments formed therein with lands extendingbetween the embossments and underlying the partitions between saidchannelways in the backplate, and a phosphor coating extending over theentire faceplate and including the areas of the lands underlying thepartitions in said backplate.

'3. A fluorescent panel lamp comprising a vitreous envelope formed by abackplate and a faceplate sealed together along their margins, saidbackplate having a plurality of grooved channelways extending thereinside by side with partitions between them and joined at alternate endsto define a labyrinthine discharge channel, said faceplate having aplurality of shallow embossments formed therein with lands extendingbetween the embossments and underlying the partitions between saidchannelways in the backplate, phosphor coatings on said plates, saidbackplate and faceplate being assembled with drainage flow patternsresulting from phosphor coating extending parallel in both plates.

4. A fluorescent panel lamp comprising a vitreous envelope formed by abackplate and a faceplate sealed together along their margins, saidbackplate having a plurality of grooved channelways extending thereinside by side with partitions between them and joined at alternate endsto define a labyrinthine discharge channel, said faceplate having aplurality of shallow embossments formed therein with lands extendingbetween the embossments and underlying the partitions between saidchannelways in the backplate, electrodes sealed into the ends of saidlabyrinthine channel, phosphor coatings on said plates, said backplateand faceplate being assembled with drainage flow patterns resulting fromphosphor coating extending parallel in both plates and with the end ofthe faceplate having a thinner phosphor coating located over theelectrodes.

5. A fluorescent panel lamp comprising a vitreous en velope formed by abackplate and a faceplate sealed together along their margins, saidbackplate having a plurality of grooved channelways extending thereinside by side with partitions between them and joined at alternate endsto define a labyrinthine discharge channel, said faceplate having aplurality of shallow em-bossments formed therein with lands extendingbetween the embossments and underlying the partitions between saidchannelways in the backplate, phosphor coatings on the inside surfacesof said plates, said backplate and faceplate being assembled withdrainage fiow patterns resulting from phosphor coating extendingparallel in both plates, said phosphor coating extending over the entirefaceplate including the areas of the lands overlying and in engagementwith the partitions in the backplate.

6. A fluorescent panel lamp comprising a vitreous envelope formed of twosheets of glass, a backplate and faceplate, sealed together along theirmargins; said backplate having a plurality of grooved channelwaysextending therein side by side and joined at alternate ends to define alabyrinthine discharge channel; said channel being formed by folds insaid backplate providing partitions between channelways with flat areasof glass at the base of contiguous partitions; said faceplate having aplurality of shallow embossments with lands extending between theembossments and underlying the fiat areas in the backplate; and aphosphor coating extending over the entire faceplate and including thelands underlying said flat areas in the backplate.

References Cited by the Examiner UNITED STATES PATENTS 2,344,081 3/ 1944Claude 1173 3.5 2,406,146 8/1946 Holmes 313-409 X 2,555,749 6/1951Kretft 313109 2,824,814 2/ 1958 Jones et al 11'733.5 2,956,150 10/1960Schwartz et al. 240-78 X 3,047,763 7/1962 Inman 3l3-109 FOREIGN PATENTS466,812 7/ 1950 Canada. 959,812 10/ 1 949 France.

GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, DAVID J. GALVIN, Examiners.

R. C. CAMPBELL, Assistant Examiner.

2. A FLUORESCENT PANEL LAMP COMPRISING A VITREOUS ENVELOPE FORMED BY ABACKPLATE AND A FACEPLATE SEALED TOGETHER ALONG THEIR MARGINS, SAIDBACKPLATE HAVING A PLURALITY OF GROOVED CHANNELWAYS EXTENDING THEREINSIDE BY SIDE WITH PARTITIONS BETWEEN THEM AND JOINED AT ALTERNATE ENDSTO DEFINE A LABYRINTHINE DISCHARGE CHANNEL, SAID FACEPLATE HAVING APLURALITY OF SHALLOW EMBOSSMENTS FORMED THEREIN WITH LANDS EXTENDINGBETWEEN THE EMBOSSMENTS AND UNDERLYING THE PARTITIONS BETWEEN SAIDCHANNELWAYS IN THE BACKPLATE, AND A PHOSPHOR COATING EXTENDING OVER THEENTIRE FACEPLATE AND INCLUDING THE AREAS OF THE LANDS UNDERLYING THEPARTITIONS IN SAID BACKPLATE.